Mutual inductance and K factor

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "J. B. Weazle McCreath by way of Terry Fritz <twftesla-at-qwest-dot-net>" <weazle-at-hurontel.on.ca>


At 01:05 PM 23/10/01 -0600, you wrote:
>
>Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<couturejh-at-telocity-dot-com>
>
>
>Weazle -
>
>Click on the following for tests of the mutual inductance and the K
>factor.  Your computer will need the Acrobat program.
>
>     http://www.mgte-dot-com/kfactor1.pdf
>or   http://www.mgte-dot-com/kfactor1.gif
>
>This test should give you the mutual inductance that agrees with the
>JHCTES Ver 3.3 TC program.  Two other tests that should be made are 
>for finding the actual operating frequency and the K Factor.
>

Hello John, coilers,

The methods and formula that you refer to above are very similar to those
used by Terry in his method of determining mutual inductance and from it,
the K factor of the coil.  I wasn't able to measure the primary current
to the degree of accuracy shown in your setup, which allows for a direct
readout of the secondary volts as being the mutual inductance.

I chose to use a value of ten amps in the primary winding, as this made
the calculations as shown below easier to do.  Listed below this are the
actual measurements that I made at four different relative positions of
the primary and secondary windings.  In my coil's construction, coupling
is varied by moving the primary up and down.

The mutual inductance is found by:  M = V / (w * I)

Where:  M = Mutual inductance in Henries.
        w = Line freq. in radians per second (377 for 60 Hz.)
        I = The measured current in the primary in amps A.C.
        V = The measured secondary voltage in volts AC.

K can then be found by using the formula:  K = M / sqrt(L1 * L2)
 
Actual measurements taken from my coil are listed below.  All where
taken with 10 amps of primary current.

  No spacers under Pri. supports: Sec. V. = .122  Mut. I. = 32.36 uH.
  0.50 " spacers                : Sec. V. = .146  Mut. I. = 38.76 uH.
  0.75 " spacers                : Sec. V. = .154  Mut. I. = 40.84 uH.
  1.00 " spacers                : Sec. V. = .162  Mut. I. = 42.97 uH.

L pri. = 0.0165 mH. (16.5 uH.), L sec. = 11.27 mH. (11,270 uH.)

  No spacers under Pri. supports: K = .075
  0.50 " spacers                : K = .089
  0.75 " spacers                : K = .095
  1.00 " spacers                : K = .100

I believe my math is correct, but as I said before, it's not one of my
strongest attributes!  I'm wondering why the my figures differ so much
from the ones generated by your program?  You already have the other
parameters of my coil, so perhaps with these additional figures I've
provided, you can retry it and see what the outcome is this time.
 



73, Weazle, VE3EAR/VE3WZL

Listening: 147.030+ and 442.075+
E-mail:    weazle-at-hurontel.on.ca
           or ve3ear-at-rac.ca
Web site:  http://www.hurontel.on.ca/~weazle